Three-dimensional printing

ABSTRACT

Methods, systems, and apparatus, including computer programs encoded on computer storage media, for working with three-dimensional object models for printing. One of the methods includes determining a plurality of infill structures in a slice of an object; and determining a path for the tool-head to create the plurality of infill structures including: determining a first portion of the path for deposition of a first infill structure during a first time period; determining a second portion of the path for deposition of one or more second infill structures that are not adjacent to the first infill structure during a second time period; and determining a third portion of the path for deposition of a third infill structure that is adjacent to the first infill structure, wherein the second time period is determined to allow the first infill structure to cool before deposition of the third infill structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. Application No. 16/838,896, entitled“THREE-DIMENSIONAL PRINTING,” filed on Apr. 2, 2020, which is adivisional of U.S. Application No. 15/433,213, entitled“THREE-DIMENSIONAL PRINTING,” filed on Feb. 15, 2017 (now U.S. Pat. No.10,639,878). The disclosures of the prior applications are consideredpart of and are incorporated by reference in the disclosure of thisapplication.

BACKGROUND

Three-dimensional (3D) printing manufacturing systems may enablecompanies to manufacture products on-demand (sometimes after receivingpayment for the product), reduce or eliminate tooling costs, launch newproducts rapidly, have faster product evolution, reduce productinventory, introduce supply chain simplification and savings, havedesign and assembly simplification via reduced part count, performmanufacturing locally, reduce shipping and waste, and increase localrecycling and material re-use.

SUMMARY

In some implementations, a three-dimensional modelling system cananalyze a three-dimensional model of a solid object that will be createdby a three-dimensional extrusion printer to determine whether and whereto add internal supports in the model so that when the object is createdthe internal supports will support hollow shell inside the object sothat a printer does not have to create a solid object, e.g., to reducethe material, print time, or both, for the object. The three-dimensionalmodelling system adds data for the hollow shell and the internalsupports to the three-dimensional model so that the three-dimensionalextrusion printer will only generate infill in the object where it isneeded instead of for an entire volume of the object. For instance, thethree-dimensional modelling system can determine whether a region of thehollow shell has an interior surface slope that does not satisfy athreshold angle, e.g., is greater than the threshold angle, and does notneed an internal support to support the hollow shell during printing ofthe object, when the object is in use, or both. When thethree-dimensional modelling system determines that the interior surfaceslope satisfies the threshold angle, the three-dimensional modellingsystem adds an interior support for the corresponding interior surface.The three-dimensional modelling system can use properties of the object,the three-dimensional extrusion printer, or both, to determine thethreshold angle.

In some implementations, a three-dimensional modelling system candetermine a print path for a tool-head in a three-dimensional extrusionprinter that has time and space separated depositions for sequentialmaterial cooling. The three-dimensional modelling system can determine aprint path that skips between non-adjacent cells or infill structures toallow a recently deposited fill line to cool before deposition of aneighboring fill line that is adjacent to the recently deposited fillline. In some implementations, the three-dimensional modelling systemcan use an open cell lattice in which sections of the object contain notoolpaths connecting unit cells. For instance, the open cell lattice canlocalize contractive forces to individual lattice struts during printingrather than realizing them over the extents of the object.

In general, one innovative aspect of the subject matter described inthis specification can be embodied in methods that include the actionsof receiving a three-dimensional model of a solid object for creation bya three-dimensional extrusion printer; determining a hollow shell forthe three-dimensional model that includes a plurality of interiorsurfaces; determining, for each of the plurality of interior surfaces,an angle of the respective interior surface; determining, for each ofthe interior surfaces that have an angle that satisfies a thresholdangle, an infill structure for an interior structure to be locatedinside a modified object and extending through each layer of thethree-dimensional model up to the respective interior surface, whereinthe modified object is the same type of object as the solid object withat least one aperture; skipping, for each of the interior surfaces thathave an angle that does not satisfy the threshold angle, generation ofany infill structure; and generating data that represents each of thedetermined infill structures for use by the three-dimensional extrusionprinter with the three-dimensional model to create the modified object.Other embodiments of this aspect include corresponding computer systems,apparatus, and computer programs recorded on one or more computerstorage devices, each configured to perform the actions of the methods.A system of one or more computers can be configured to performparticular operations or actions by virtue of having software, firmware,hardware, or a combination of them installed on the system that inoperation causes or cause the system to perform the actions. One or morecomputer programs can be configured to perform particular operations oractions by virtue of including instructions that, when executed by dataprocessing apparatus, cause the apparatus to perform the actions.

In general, one innovative aspect of the subject matter described inthis specification can be embodied in methods that include the actionsof receiving a three-dimensional model of an object to be created by athree-dimensional extrusion printer that includes a tool-head that willcreate at least a portion of the object; determining a plurality ofinfill structures in a slice of the object, the infill structuresincluding a first infill structure, one or more second infill structuresthat each are not adjacent to the first infill structure in the slice,and a third infill structure that is adjacent to the first infillstructure in the slice; and determining a path for the tool-head tocreate each of the plurality of infill structures in the slice of theobject including: determining a first portion of the path to cause thetool-head to deposit material forming the first infill structure duringa first time period; determining a second portion of the path to causethe tool-head to deposit material forming each of the second infillstructures that are not adjacent to the first infill structure during asecond time period after the first time period; and determining a thirdportion of the path to cause the tool-head to deposit material formingthe third infill structure that is adjacent to the first infillstructure during a third time period after the second time period,wherein the second time period is determined to allow the first infillstructure to cool before deposition of the third infill structure by thetool-head of the three-dimensional extrusion printer. Other embodimentsof this aspect include corresponding computer systems, apparatus, andcomputer programs recorded on one or more computer storage devices, eachconfigured to perform the actions of the methods. A system of one ormore computers can be configured to perform particular operations oractions by virtue of having software, firmware, hardware, or acombination of them installed on the system that in operation causes orcause the system to perform the actions. One or more computer programscan be configured to perform particular operations or actions by virtueof including instructions that, when executed by data processingapparatus, cause the apparatus to perform the actions.

The foregoing and other embodiments can each optionally include one ormore of the following features, alone or in combination. Receiving thethree-dimensional model of the solid object to be created by thethree-dimensional extrusion printer may include receiving thethree-dimensional model of the solid object to be created by a fusedfilament fabrication printer. The method may include comparing, for eachof the plurality of interior surfaces of the modified object, the angleof the respective interior surface with the threshold angle;determining, for each interior surface in a first subset of the interiorsurfaces, that the angle of the respective interior surface satisfiesthe threshold angle; and determining, for each interior surface in asecond subset of the interior surfaces, that the angle of the respectiveinterior surface does not satisfy the threshold angle, the second subsetbeing a different, disjoint subset of the interior surfaces than thefirst subset. Determining, for each of the interior surfaces that havean angle that satisfies the threshold angle, the infill structure forthe interior structure to be located inside the modified object andextending through each layer of the three-dimensional model up to therespective interior surface may include determining, for each of theinterior surfaces in the first subset, the infill structure for theinterior structure to be located inside the modified object andextending through each layer of the three-dimensional model up to therespective interior surface in response to determining that the angle ofthe respective interior surface satisfies the threshold angle. Skipping,for each of the interior surfaces that have an angle that does notsatisfy the threshold angle, generation of any infill structure mayinclude skipping, for each of the interior surfaces in the secondsubset, generation of any infill structure in response to determiningthat the angle of the respective interior surface does not satisfy thethreshold angle.

In some implementations, the method may include determining aconfiguration of the three-dimensional extrusion printer; determining amaterial that the three-dimensional extrusion printer will use to createthe modified object; and determining the threshold angle using theconfiguration and a property of the material. The method may includedetermining a material that the three-dimensional extrusion printer willuse to create the modified object; and determining the threshold angleusing a property of the material. The method may include determining aconfiguration of the three-dimensional extrusion printer; anddetermining the threshold angle using the configuration.

In some implementations, the method may include generating a pluralityof slices of the three-dimensional model that each identify one or moresurfaces for the modified object represented by the respective slice inresponse to generating data that represents each of the determinedinfill structures for use by the three-dimensional extrusion printerwith the three-dimensional model to create the modified object;generating, for each of the plurality of slices, tool path data thatindicates a path for a tool-head included in the three-dimensionalextrusion printer to create the one or more surfaces represented by therespective slice; and providing, for at least one of the plurality ofslices, the tool path data to the three-dimensional extrusion printer.Receiving the three-dimensional model of the object to be created by thethree-dimensional extrusion printer may include receiving thethree-dimensional model of the object to be created by a fused filamentfabrication printer. The method may include determining a material thatthe three-dimensional extrusion printer will use to create the object;determining a cooling time for the material using a first temperature atwhich the material will be deposited and at least one second temperatureof an area in which the material will be deposited; and determining aduration for the second time period using the cooling time for thematerial. The method may include determining a material that thethree-dimensional extrusion printer will use to create the object;determining a property of the material; and determining a length of thefirst portion of the path using the property of the material. The methodmay include determining a material that the three-dimensional extrusionprinter will use to create the object; determining a property of thematerial; and determining a deposition rate for the first portion of thepath using the property of the material.

In some implementations, determining the path for the tool-head tocreate each of the plurality of infill structures may includedetermining, for all infill structures in the plurality of infillstructures for which a portion of the path has not been determined, arespective portion of the path during a period of time separated in timefrom the time periods for the infill structures adjacent to therespective infill structure to allow the adjacent infill structures tocool before deposition of the respective infill structure. Determiningthe second portion of the path to cause the tool-head to depositmaterial forming each of the second infill structures that are notadjacent to the first infill structure during the second time periodafter the first time period may include determining the second portionof the path to cause the tool-head to deposit material forming each oftwo or more second infill structures that are not adjacent to the firstinfill structure during the second time period after the first timeperiod. The method may include generating the slice of the object thatidentifies one or more surfaces for the object represented by therespective slice; and providing, for the slice of the object, tool pathdata that indicates the path for the tool-head to create the slice ofthe object to the three-dimensional extrusion printer.

The subject matter described in this specification can be implemented inparticular embodiments and may result in one or more of the followingadvantages. In some implementations, a modelling system may reduce anamount of material necessary to print an object, reduce an amount oftime necessary to print the object, or both, by creating internalsupports where needed compared to other systems. In someimplementations, a modelling system that generates a tool-head printpath which has time and space separated fill line depositions mayalleviate internal forces that induce warping in the fill lines whilethe fill lines cool. In some implementations, a modelling system may usean open cell lattice to localize contractive forces to individuallattice struts during printing, e.g., rather than realizing them overthe extents of the object. In some implementations, when a modellingsystem determines a path that allows a deposited material in a region tocool and potentially contract, the modelling system may reduce alikelihood that the deposited material in a region will pull away frommaterial in an adjacent region while the material in the two regionscool.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the description below. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B are an example of a three-dimensional model of an object thatcan be printed by a three-dimensional extrusion printer.

FIG. 2 is an example of a slice of a three-dimensional model for anobject.

FIG. 3 is an example of an environment in which a three-dimensionalmodelling system may receive a three-dimensional model.

FIG. 4 is a flow diagram of a process for generating data for infillstructures that will support surfaces of an object.

FIG. 5 is a flow diagram of a process for generating a tool-head path.

FIG. 6 is a block diagram of a computing system that can be used inconnection with computer-implemented methods described in this document.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIGS. 1A-B are an example of a three-dimensional model 100 of an objectthat can be printed by a three-dimensional extrusion printer. Athree-dimensional modelling system may receive the three-dimensionalmodel 100 of a solid object that will be created by a three-dimensionalprinter and analyze the solid object to determine whether to include anyhollow portions within the object, e.g., to reduce material, print time,or both, for the object.

The three-dimensional modelling system may create a hollow shell insidethe three-dimensional model 100. For instance, the three-dimensionalmodelling system may analyze the three-dimensional model to determinewhether to print a hollow shell of the object instead of a solid object.The hollow shell can include multiple skins 101 a, multiple perimeters101 b, or both, that form an exterior of the object. In FIG. 1A some ofthe multiple perimeters 101 b are labeled. In some examples, all of thecircular objects may similarly indicate other perimeters that form thehollow shell.

The three-dimensional modelling system analyze angles of the interiorsurfaces of the hollow shell to determine whether and where to place aninfill structure that will support the interior surface of the hollowshell. The three-dimensional modelling system may compare each interiorsurface angle of the hollow shell with a threshold angle to determinewhether the interior surface angle satisfies the threshold angle, e.g.,is less than or equal to the threshold angle or is less than thethreshold angle. The surfaces may be polygon meshes that represent thehollow shell or other surfaces for the hollow shell.

The three-dimensional modelling system may generate the hollow shell andanalyze the interior surface angles formed by the hollow shell. Thethree-dimensional modelling system may determine whether the hollowshell, and any interior infill structures that will support part of thehollow shell, provide sufficient support for the object, e.g., whether astrength of a modified object would satisfy a threshold strength for theobject. The three-dimensional modelling system may determine thethreshold strength using properties of the material that will be used tocreate the object, expected pressures that may be applied to the object,or another appropriate value. The three-dimensional modelling system maydetermine whether the hollow shell, and any interior infill structures,satisfy a threshold reduction in material necessary to create a modifiedobject. When the three-dimensional modelling system determines that thehollow shell, and any interior infill structures, do not satisfy athreshold, the three-dimensional modelling system may determine that theentire solid object should be printed and send data for the entire solidobject to a printer. When the three-dimensional modelling systemdetermines that the hollow shell, and interior infill structures,satisfy the threshold, the three-dimensional modelling system may senddata for the hollow shell and the interior infill structures to aprinter, e.g., to cause the printer to create a modified version of theobject using the hollow shell and the interior infill structures.

The object may be any appropriate type of object that can be created bya three-dimensional extrusion printer for which the three-dimensionalmodelling system receives a three-dimensional model of a solid object.For instance, the three-dimensional modelling system may receive athree-dimensional scale model 100 of a block. The block may be a toywith which a child will play. In some examples, the block may be usedfor construction, e.g., building a house.

As referred to in this document, an exterior surface in athree-dimensional model is a surface that forms an exterior boundary ofthe three-dimensional model. An interior surface in thethree-dimensional model is a surface that is bounded by multipleexterior surfaces of the three-dimensional model, e.g., that issurrounded on all sides by exterior surfaces.

The three-dimensional modelling system may determine an angle of asurface with respect to a three-dimensional extrusion printer print bedon which the object will be created. For example, the three-dimensionalmodelling system may determine that a bottom 102 of the block will bepositioned on the print bed and determines the angles of surfaces withrespect to the bottom 102.

The three-dimensional modelling system may analyze each of the walls ofthe hollow shell, such as a wall 104, to determine whether an angle ofthe wall satisfies the threshold angle. The wall 104 may includemultiple perimeters 101 b shown on the right hand side of thethree-dimensional model 100. The three-dimensional modelling system mayselect the wall 104 and determine a particular angle 105 of the wall104. In the example shown, the three-dimensional modelling system maydetermine that the particular angle 105 is ninety degrees.

The three-dimensional modelling system compares the particular angle 105with the threshold angle. For instance, the three-dimensional modellingsystem may determine a material that will be used to create the wall104, a configuration of the three-dimensional extrusion printer thatwill create the block, or both, to determine the threshold angle. Thethree-dimensional modelling system compares the value for the particularangle 105 with the value for the threshold angle. The three-dimensionalmodelling system determines that the particular angle 105 of the wall104 does not satisfy the threshold angle, e.g., that ninety degrees isgreater than the threshold angle, and that the three-dimensionalmodelling system does not need to create an infill structure to supportthe wall 104.

In some implementations, the three-dimensional modelling system maydetermine whether to adjust a value for the angle of the surfaces in thethree-dimensional model 100, e.g., if the angle is outside apredetermined range of angles. For example, the three-dimensionalmodelling system may use a predetermined range of angles between zeroand ninety degrees, inclusive. The three-dimensional modelling systemcan determine whether the angle of a surface is between zero and ninetydegrees, inclusive. When a value of the angle is not between zero andninety degrees, inclusive, the three-dimensional modelling system mayadjust the value of the angle. For instance, the three-dimensionalmodelling system may determine an adjusted value for the angle that isbetween zero and ninety degrees, inclusive, that is the equivalent ofthe current value of the angle. When the angle is one-hundred eightydegrees, the three-dimensional modelling system may change the value ofthe angle to zero degrees. When the angle is one-hundred thirty-fivedegrees, the three-dimensional modelling system may change the value ofthe angle to forty-five degrees. When the angle is ninety-nine degrees,the three-dimensional modelling system may change the value of the angleto eighty-one degrees.

In some implementations, when the three-dimensional modelling systemdetermines that the angle is between zero and ninety degrees, inclusive,the three-dimensional modelling system compares the angle with thethreshold angle to determine whether the angle satisfies the thresholdangle. In some examples, the angle may satisfy the threshold angle whenthe angle is less than the threshold angle. The angle may satisfy thethreshold angle when the angle is less than or equal to the thresholdangle. When a value of the angle is zero, e.g., when the surface isparallel to the print bed, the three-dimensional modelling system maydetermine a distance between the surface and the print bed. When thedistance is zero, the three-dimensional modelling system determines toskip generation of an infill structure to support the surface. When thedistance is greater than zero, the three-dimensional modelling systemdetermines to generate an infill structure to support the surface. Whena value of the angle is non-zero and satisfies the threshold angle, thethree-dimensional modelling system may generate an infill structure tosupport the surface. When a value of the angle does not satisfy thethreshold angle, the three-dimensional modelling system skips generationof an infill structure to support the surface.

The three-dimensional modelling system may analyze an upper section 106a-b of the hollow shell to determine whether an angle for the uppersection 106 a-b satisfies a threshold angle. For instance, thethree-dimensional modelling system may analyze a first upper section 106a separately from a second upper section 106 b when both the first uppersection 106 a and the second upper section 106 b are above the walls 104of the hollow shell for the block.

The three-dimensional modelling system determines a first angle 107 forthe first upper section 106 a and compares the first angle 107 with thethreshold angle. For instance, the three-dimensional modelling systemdetermines whether the first angle 107 is less than or equal to thethreshold angle. In some examples, the three-dimensional modellingsystem may determine whether the first angle 107 is less than thethreshold angle.

The three-dimensional modeling system uses the comparison of the anglesto determine whether the first angle 107 satisfies the threshold angle.For example, the three-dimensional modelling system determines that thefirst angle 107 does not satisfy the threshold angle. In response todetermining that the first angle 107 does not satisfy the thresholdangle, the three-dimensional modelling system may determine to skipgeneration of an infill structure that will support the first uppersection 106 a. For instance, the three-dimensional modelling systemdetermines not to generate an infill structure in the three-dimensionalmodel 100 that will support the first roof upper 106 a.

The three-dimensional modelling system may determine that a second angleof the second upper section 106 b is the same as the first angle 107 ofthe first upper section 106 a. The three-dimensional modelling systemmay determine, in response, to skip generation of an infill structurethat will support the second upper section 106 b. In some examples, thethree-dimensional modelling system may compare the second angle of thesecond upper section 106 b with the threshold angle to determine whetherto generate an infill structure that will support the second uppersection 106 b.

The hollow shell includes a top section 108. The three-dimensionalmodelling system may compare a third angle 109 of the top section 108with a threshold angle to determine whether the respective anglesatisfies the threshold angle.

The three-dimensional modelling system may compare the third angle 109for the top section 108 with the threshold angle. Using the comparison,the three-dimensional modelling system may determine whether the thirdangle 109 for the top section 108 satisfies the threshold angle. Thethree-dimensional modelling system may determine that the third angle109 satisfies the threshold angle, e.g., that the third angle 109 isless than the threshold angle or that the third angle 109 is less thanor equal to the threshold angle. In response, the three-dimensionalmodelling system may determine to generate an infill structure 110,shown in FIG. 1B, to support the top section 108. The infill structure110 creates one or more apertures 112 inside the hollow shell. Theapertures 112 represent the portion of the object that will not need toinclude fill material, e.g., for which a three-dimensional printer doesnot need to deposit material to create the object.

The three-dimensional modelling system creates an infill structure thatfills only a portion of the area inside the hollow structure that isbelow the top section 108. For instance, the three-dimensional modellingsystem may analyze the size of the top section 108, the third angle 109,the material a three-dimensional printer will use to create the topsection 108, or a combination of two or more of these to determine asize of the infill structure 110 that is smaller than the entire regionbelow the top section 108 and inside the hollow structure. Thethree-dimensional modelling system may determine the infill structure110 such that the infill structure 110 does not lie below either of theupper sections 106 a-b, as indicated by dashed line 114. For instance,dashed line 114 indicates the right hand side of the infill structure110 so that the infill structure 110 does not lie below the first uppersection 106 a. The dashed line 114 is not included in data for thethree-dimensional model 100. For example, the three-dimensionalmodelling system includes the hollow structure, e.g., the skins 101 aand the perimeters 101 b, and the infill structure 110 in data for thethree-dimensional model, e.g., and does not include any data specificonly to the line 114 in the data for the three-dimensional model.

The three-dimensional modelling system may determine a type of theinfill structure 110 to support the top section 108, e.g., in responseto determining that the third angle 109 satisfies the threshold angle.For instance, the three-dimensional modelling system may use propertiesof the material that will be used to create the top section 108,properties of the three-dimensional extrusion printer that will createthe block, or both, to determine a type of the infill structure 110. Thethree-dimensional modelling system may select a first type of infillstructure 110 when the third angle 109 falls within a first angle range,e.g., twenty and thirty degrees. The first type may be a pillar, aparticular material for the infill structure 110, or both. Thethree-dimensional modelling system may select a second type of infillstructure 110 when the third angle 109 falls within a second anglerange, e.g., when the third angle is zero and the respective surface isparallel to and separated from the print bed, such as the example shownin FIG. 1A. The second type of infill structure 110 may be a completefill between the bottom 102 of the block and the top section 108, alattice framework of fill lines that, when stacked in layers of latticesbetween the bottom 102 and the top section 108, support the top section108, a hexagonal fill, or another appropriate type of infill structure110.

The three-dimensional modelling system may determine a type of infillstructure 110 by balancing the material necessary to support the topsection 108 with a time necessary to deposit the material. For instance,the three-dimensional modelling system may minimize a quantity ofmaterial for the infill structure 110, a time necessary to deposit thematerial, e.g., when a more elaborate infill structure 110 may requireless material but take more time to create, or both.

In some implementations, the three-dimensional modelling system may havemultiple different threshold angles. For instance, the three-dimensionalmodelling system may determine a threshold angle for each type ofmaterial that will be used to create a surface in the object representedby the three-dimensional model 100. The three-dimensional modellingsystem may use i) properties of the material or ii) properties of thematerial and properties of a three-dimensional extrusion printer thatwill create the object to determine a corresponding threshold angle. Forexample, the three-dimensional modelling system may have a firstthreshold angle for a surface that will be created from plastic and asecond threshold angle for a surface that will be created from metal. Insome examples, the three-dimensional modelling system may use a firstthreshold angle for the wall 104, a second threshold angle for the firstupper section 106 a, and a third threshold angle for the top section108. In some examples, the three-dimensional modelling system may use afirst threshold angle for the wall 104, and a second threshold angle forthe first upper section 106 a and the top section 108.

When the three-dimensional modelling system analyzes a surface that willbe adjacent to the print bed of the three-dimensional extrusion printer,e.g., a bottom 102, the three-dimensional modelling system may determineto skip generation of an infill structure for the bottom 102 withoutcomparing an angle of the bottom 102 to a threshold angle. For instance,the three-dimensional modelling system may determine that the bottom 102will be supported by the print bed and that no infill structures arenecessary to support the bottom 102 or that no infill structures insidethe object can be created to support the bottom 102.

In some implementations, the three-dimensional model 100 may be for asolid object that will be included in another object. For instance, theblock may be part of a larger toy, a model of a house, or another typeof object. The three-dimensional modelling system may analyze the blockto determine whether the block can be created using a hollow shell andinclude the block with a hollow shell in the other object.

In some examples, the three-dimensional modelling system may analyze aslice of the block shown in FIGS. 1A-B to determine a path for anextrusion printer tool-head to create an object using thethree-dimensional model 100. For instance, after the three-dimensionalmodelling system creates data for the hollow shell and the infillstructure, the three-dimensional modelling system may analyze each sliceof the block to determine a path for the tool-head to create the hollowblock.

FIG. 2 is an example of a slice 200 of a three-dimensional model for anobject. The object may be any appropriate type of object that can becreated by a three-dimensional extrusion printer. For instance, thethree-dimensional modelling system may receive a three-dimensional scalemodel of a house with an attached garage, generally referred to as ahouse in this document. The house may be a toy house with which a childwill play. The house may be an architectural model of a house that willbe built or remodeled, or another appropriate type of architecturalmodel. For example, the scale model of a house may be used as a toy intowhich a person will not walk.

A three-dimensional modelling system may analyze the slice 200 todetermine a path for a three-dimensional extrusion printer tool-headthat indicates an order in which the tool-head should deposit material,e.g., fill lines, for various structures in the slice 200. For instance,the three-dimensional modelling system may analyze multiple regions202-210 of internal structures to determine a path for a tool-head tocreate the internal structures in each of the regions 202-210 whileallowing material deposited to form the respective structure to coolbefore deposition of internal structures in an adjacent region. Theregions 202-210 are depicted in FIG. 2 by the dashed lines. Thethree-dimensional modelling system may split the slice 200 into regionsfor separate printing of each of the regions so that forces in each ofthe regions, created because of the printing of materials in therespective region, manifest at a smaller spatial scale. Themanifestation of forces at a smaller spatial scale may reduce alikelihood of material in any of the regions 202-210 warping.

The three-dimensional modelling system may determine the path for atool-head included in a three-dimensional extrusion printer that willcreate the object using the slice 200. In some examples, thethree-dimensional modelling system creates a path for a tool-headincluded in a fused filament fabrication three-dimensional extrusionprinter.

The path for the tool-head moves between the regions 202-210 of internalstructures to allow all material deposited in a particular region tocool before deposition of material in an adjacent region to reduce alikelihood that material deposited in the particular region will warp,pull away from material in an adjacent region, or both. For instance, asa material cools, the material may contract. The three-dimensionalmodelling system determines time periods for the regions 202-210 thatallow the material in the respective region to cool, and potentiallycontract, before a tool-head will deposit material in an adjacentregion.

The three-dimensional modelling system may determine a property of amaterial, a property of a three-dimensional extrusion printer that willprint the material, or both, to determine a time period for a regionthat allows a material in the region to cool. For instance, thethree-dimensional modelling system may determine a cooling rate for amaterial based on an ambient temperature of a three-dimensionalextrusion printer. The three-dimensional modelling system may use thecooling rate to determine a time period for the region that allows thematerial to completely cool or a time period that allows the material tocool to a point at which an amount that the material may contract isless than a threshold amount, a likelihood that the material willcontract more is less than a threshold likelihood, or both.

In some implementations, the three-dimensional modelling system maydetermine a time period for a region using an amount of materialdeposited in the region. For instance, the three-dimensional modellingsystem may select a longer time period for a region in which morematerial will be deposited compared to a shorter time period for adifferent region in which less material will be deposited.

For the slice 200, a three-dimensional modelling system may select afirst region 202 for the beginning of a tool-head path. Thethree-dimensional modelling system may determine that the tool-headshould deposit material for a first structure 212 in the first region202 and then a second structure 214 in the first region. Thethree-dimensional modelling system determines a first time periodnecessary to allow the material for the first structure 212 and thematerial for the second structure 214 to cool.

The three-dimensional modelling system analyzes one or more of the otherregions 204-210 to determine a region that is not adjacent to the firstregion 202 and that will be the next region for the tool-head path. Forinstance, the three-dimensional modelling system may determine thatthree regions 206-210 are not adjacent to the first region 202 andselect one of the three regions 206-210. The three-dimensional modellingsystem may select a fourth region 208.

The three-dimensional modelling system determines one or more structuresin the selected fourth region 208. For instance, the three-dimensionalmodelling system may determine that the fourth region 208 includes afifth structure 220. The three-dimensional modelling system may generatea path for the tool-head to deposit material for the fifth structure220.

The three-dimensional modelling system may select a deposition rate forthe tool-head to deposit the material for the fifth structure 220 usingthe first time period to allow the material for the first structure 212and the material for the second structure 214 to cool. For instance, thethree-dimensional modelling system may select a deposition rate so thata length of time for the tool-head to deposit the material for the fifthstructure 220 is the same as the duration of the first time period. Thethree-dimensional modelling system may select a deposition rate so thatthe length of time for the tool-head to move to the fifth structure 220,move away from the fifth structure 220, and deposit the material for thefifth structure 220 is the same as the duration of the first timeperiod.

In some examples, the three-dimensional modelling system may select adeposition rate for the fourth region 208 so that a time necessary todeposit material in multiple regions is equal to the duration of thefirst time period. For example, the three-dimensional modelling systemmay select a deposition rate for the fifth structure 220 so that a sumof a second time period during which the tool-head will deposit thematerial for the fifth structure 220 and a third time period duringwhich the tool-head will deposit material for a sixth structure 222 inthe fifth region 210 will total the duration of the first time period.The sum of the second time period and the third time period may includedurations for the tool-head to move to the fifth structure 220, to moveto the sixth structure 222, to move away from the sixth structure, or acombination of two or more of these.

Once the three-dimensional modelling system has updated the path for thetool-head to include deposition of one or more structures during thefirst time period, the three-dimensional modelling system selects aregion that is adjacent to the first region 202. The three-dimensionalmodelling system may select a second region 204 and determine portionsof the path for the tool-head to create a third structure 216 includedin the second region. The three-dimensional modelling system maydetermine multiple fill lines for the tool-head to create the thirdstructure 216 and corresponding portions of the path for those multiplefill lines.

The three-dimensional modelling system may select fill lines for thethird structure 216 using a type of infill for the third structure 216.For instance, when the third structure 216 has a lattice infill, thethree-dimensional modelling system may determine a first set of pathsfor the tool-head to create the third structure 216 and add the firstset of paths to the overall path for the tool-head to create the slice200. When the third structure 216 has a hexagonal infill, thethree-dimensional modelling system may determine a second set of pathsfor the tool-head to create the third structure 216 and add the secondset of paths to the overall path for the tool-head to create the slice200 instead of the first set of paths. The first set of paths for thetool-head may be different paths than the second set of paths for thetool-head. The third structure 216, and the other structures in theslice 200, may have any appropriate infill structure.

In some implementations, the three-dimensional modelling system may usean open cell lattice infill in which X-Y sections contain no toolpathsconnecting unit cells. The unit cells may be one of the structures212-222, may be a portion of one of the structures 212-222, e.g., a beaddeposited for one of the structures 212-222, or both. Thethree-dimensional modelling system may have one or more settings thatdefine properties for the unit cells. For instance, the properties mayinclude a maximum area for a unit cell, a maximum length, maximum width,or both, for the unit cell, a maximum bead length, or a combination oftwo or more of these.

The use of an open cell lattice infill may localize contractive forceson the unit cells. For instance, as a deposited bead of material cools,the bead will contract to a percentage of its original length. Thepercentage of the original length for the cooled bead may be determinedusing a change in the temperature of the bead when deposited to a cooledtemperature and the coefficient of thermal expansion for the material ofthe bead. By depositing smaller beads, e.g., for unit cells, thestructures 212-222, or both, that are allowed to cool before materialdeposition for an adjacent bead, a three-dimensional modelling systemreduces the total size of the shrinkage. For example, when a temperaturechange, e.g., from 230° C. to 30° C., will cause a deposited bead toshrink by 2%, a bead that is 10 millimeters (mm) long will shrink 0.2 mmwhile a bead that is 100 mm long will shrink 2 mm, the latter of whichmay cause a gap between deposited materials. When the three-dimensionalmodelling system uses an open cell lattice infill, the three-dimensionalmodelling system reduces localizes contractive forces and reduces anamount of contraction for deposited beads. This may allow thethree-dimensional modelling system to maintain cooling shrinkage amountsto a manageable level at which there will be minimal gaps betweendeposited materials.

The three-dimensional modelling system selects a third region 206 as thelast region for the path. The three-dimensional modelling systemgenerates portions of the path for deposition of a fourth structure 218.For instance, the three-dimensional modelling system determines thatthere are no regions left in the slice 200 for which thethree-dimensional modelling system has not generated a respectiveportion of the path other than the third region 206 and selects thethird region 206.

The three-dimensional modelling system may determine whether a fourthtime period for cooling of the fifth structure 220 included in thefourth region 208 will pass before deposition of structures in the thirdregion 206 based on the tool-head path. For example, thethree-dimensional modelling system may determine whether the fifthstructure 220 will sufficiently cool given the tool-head path to allowdeposition of the fourth structure 218 in the third region 206. When thethree-dimensional modelling system determines that the fourth timeperiod will pass given the tool-head path, the three-dimensionalmodelling system generates the portions of the path for deposition ofthe fourth structure 218.

When the three-dimensional modelling system determines that the fourthtime period will not pass given the tool-head path, thethree-dimensional modelling system determines whether to generate adifferent path for creation of structures 212-222 in the slice 200. Forinstance, when the path includes generation of structures in the fifthregion 210 before generation of structures in the fourth region 208, thethree-dimensional modelling system may change an order of portions ofthe path by including a portion of the path for the fourth region 208before a portion of the path for the fifth region 210. When thethree-dimensional modelling system changes the order of portions of thepath, the three-dimensional modelling system may determine that the neworder of the portions of the path will allow the fifth structure 220 inthe fourth region 208 sufficient time to cool before deposition of thefourth structure 218 in the third region 206, which is adjacent to thefourth region 208. When the three-dimensional modelling systemdetermines that a new order of the portions of the path that correspondto respective regions 202-210 in the slice 200 does not allow sufficienttime for the various structures 212-222 in the regions 202-210 to coolbefore deposition of material in an adjacent region, thethree-dimensional modelling system may change one or more depositionrates for some or all of the structures 212-222 so that the pathincludes sufficient time for each of the structures in a particularregion to cool before deposition of a structure in an adjacent region.

Each of the regions 202-210 may include a single structure, a portion ofa structure, or multiple structures. For instance, the first region 202includes two structures, the first structure 212 and the secondstructure 214, and the second region 204 includes one structure, thethird structure 216. In some examples, the first structure 212 may be inone region and the second structure 214 may be in a separate region.

A three-dimensional printer may create the structures 212-222 using thesame material or different materials. For example, the first structure212, the second structure 214, and the third structure 216 may becreated using the same material and are shown separately in FIG. 2 toindicate different portions of the path generated by thethree-dimensional modelling system. In some examples, athree-dimensional printer may create the first structure 212 and thesecond structure 214 from a particular material and may create the thirdstructure 216 from a different material.

The three-dimensional modelling system may generate, for each of theregions, a respective portion of the tool-head path for multiple filllines that will be deposited in the region. For example, thethree-dimensional modelling system may create a first portion of thetool-head path for the first region 202 that will cause a tool-head todeposit twelve fill lines to create the first structure 212 and thesecond structure 214. The three-dimensional modelling system may createa second portion of the tool-head path for the second region 204 thatwill cause a tool-head to deposit four fill lines to create the thirdstructure 216.

In some examples, the regions 202-210 for which the three-dimensionalmodelling system generates portions of the tool-head path may beinterior regions. The regions may include infill structures or portionsof infill structures. The regions for which the three-dimensionalmodelling system generates portions of the tool-head path may beexterior regions.

In some implementations, the three-dimensional modelling system canautomatically determine the regions 202-210. For instance, thethree-dimensional modelling system can receive the slice 200 anddetermine an initial region for the slice, e.g., that include an entireinterior for the slice 200. The three-dimensional modelling system cangenerate smaller regions from the initial region to reduce a likelihoodthat material deposited for structures in the region will move whenadjacent material is deposited for the slice. The three-dimensionalmodelling system can use a predetermined maximum size for each region orcan automatically determine a size for each of the sub-regions.

In some implementations, the three-dimensional modelling system maydetermine a maximum fill line length. For example, the three-dimensionalmodelling system may determine sizes for each of the regions such thatthe fill lines in each of the regions do not exceed the maximum fillline length. The three-dimensional modelling system may determine sizesof the regions to minimize contraction between fill lines in adjacentregions. For instance, the three-dimensional modelling system maydetermine sizes of the regions using the maximum fill line length, e.g.,as a maximum length, width, or both. The three-dimensional modellingsystem may adjust one or more dimensions of the regions to minimizecontraction between fill lines in adjacent regions. For example, whenthe structures in the first region 202 and the second region 204 will becreated using a single material, the three-dimensional modelling systemmay determine a point 224 in the first region 202 that will minimize alength of a border between structures in the first region 202 andstructures in the second region 204. The three-dimensional modellingsystem may move the right border of the second region 204 to the point224 to reduce the length of contact between the fill lines, andcorresponding structures, in the adjacent regions.

The three-dimensional modelling system may use a type of material forstructures in a region when determining the regions. For instance, ifthe three-dimensional modelling system determines that a single materialwill be used to create the first structure 212, the second structure214, and the third structure 216, the three-dimensional modelling systemmay adjust the size of the regions, e.g., to minimize contact betweenthe structures in the regions. If the three-dimensional modelling systemdetermines that different materials will be used to create thestructures in the first region 202 and the second region 204, e.g., thata first material will be deposited for the first structure 212 and thesecond structure 214 and a second material will be deposited for thethird structure 216, the three-dimensional modelling system may maintainthe sizes of the first region 202 and the second region 204.

In some implementations, a three-dimensional modelling system maydetermine a time for a tool-head to move between regions and use thetime to determine a path for the tool-head. For instance, thethree-dimensional modelling system may use the time for the tool-head tomove between regions to allow material in a region enough time to cool.The three-dimensional modelling system may use the movement time inaddition to the deposition time to determine the path for the tool-headand whether the three-dimensional modelling system can select a regionfor deposition that is adjacent to another region in which depositedmaterial has cooled.

In some implementations, the three-dimensional modelling system maydetermine different cooling rates for different materials in a slice.For instance, the three-dimensional modelling system may determine thata first structure 212 is metal and a third structure 216 is plastic anddifferent cooling rates for the first structure 212 and the thirdstructure 216. The three-dimensional modelling system may determinedifferent time periods for the regions in which the structures belong toallow the structures sufficient time to cool.

FIG. 3 is an example of an environment 300 in which a three-dimensionalmodelling system 302 may receive a three-dimensional model 304. Thethree-dimensional modelling system 302 may receive the three-dimensionalmodel 304 from a client device 316. For example, the three-dimensionalmodelling system 302 may receive the three-dimensional model 304 as partof a request from the client device 316 to cause a three-dimensionalextrusion printer 318 to create an object represented by thethree-dimensional model 304. In some examples, the three-dimensionalextrusion printer 318 may be a fused filament fabrication printer.

The three-dimensional modelling system 302 may determine materials thatwill be used to create an object represented by the three-dimensionalmodel 304. The three-dimensional modelling system 302 may select aparticular type of three-dimensional extrusion printer 318 usingproperties of the materials in the material properties database 314, thematerials, or both. For example, the three-dimensional modelling system302 may provide the three-dimensional model 304 to a fused filamentfabrication printer when the object represented by the three-dimensionalmodel 304 will be formed using a material or multiple materials with ahigh coefficient of thermal expansion.

An angle generation module 306, included in the three-dimensionalmodelling system 302, may generate, for a solid object or a solidportion of an object, a hollow shell for the object. The anglegeneration module 306 may analyze the exterior surfaces of the objectthat enclose the solid fill for the object to determine the hollow shellfor the object. The angle generation module 306 may determine a minimumthickness of the hollow shell using properties of the object, e.g., amaterial of the object, expected forces that will be applied to theobject, or both. The angle generation module 306 may determine differentthicknesses for different portions of the hollow shell depending on thelocation of the portion in the hollow shell. The angle generation module306 may update the three-dimensional model 304 using data thatrepresents the hollow shell for the object.

The angle generation module 306 analyze multiple surfaces in the hollowshell to determine angles of those surfaces. The angle generation module306 may determine angles of the surfaces with respect to a print bed onwhich an object, represented by the three-dimensional model 304, will becreated by the three-dimensional extrusion printer 318. For instance,the angle generation module 306 may perform one or more of the stepsdescribed above with reference to FIGS. 1A-B to determine an angle of anexterior surface, an interior surface, or both. In some examples, theangle generation module 306 may determine a threshold angle. Thethreshold angle may be for all surfaces in the object or a subset of thesurfaces in the object, e.g., when all of the surfaces in the subsetwill be created by the three-dimensional extrusion printer 318 using aparticular material and all surfaces in a different subset will becreated by the three-dimensional extrusion printer 318 using a differentmaterial.

A surface analysis module 308 compares the angles determined by theangle generation module 306 with respective threshold angles todetermine whether to generate a support for the respective surface inthe three-dimensional model 304. For example, when the surface analysismodule 308 determines that a first angle of a first surface does notsatisfy a threshold angle, the surface analysis module 308 skips thefirst surface and does not generate a support for the first surface.When the surface analysis module 308 determines that a second angle of asecond surface satisfies a threshold angle, the surface analysis module308, or a support generation module (not shown) included in thethree-dimensional modelling system 302, generates data for a support inthe three-dimensional model 304. The support is an infill structure,inside the hollow shell of the object represented by thethree-dimensional model 304, that will support the second surface duringcreation of the object by the three-dimensional extrusion printer 318and during use of the created object. The surface analysis module 308may perform one or more of the steps described above with reference toFIGS. 1A-B to compare the surface angles with the threshold angles andgenerate supports for the surfaces for which the surface angle satisfiesa corresponding threshold angle.

The angle generation module 306 or the surface analysis module 308 candetermine a threshold angle. For instance, the surface analysis module308 may determine a material that will be used to create a particularsurface. The surface analysis module 308 accesses a material propertiesdatabase 314 to determine properties for the material. The surfaceanalysis module 308 can use the properties for the material to determinethe threshold angle for the material.

In some implementations, the surface analysis module 308 usesconfiguration properties of the three-dimensional extrusion printer 318when determining the threshold angle. For example, the surface analysismodule 308 may access a three-dimensional printer configuration database312 to determine configuration properties for the three-dimensionalextrusion printer 318, e.g., using an identifier for thethree-dimensional extrusion printer 318. The surface analysis module 308may use the configuration properties and the properties for the materialto determine the threshold angle for the material.

A path generation module 310, included in the three-dimensionalmodelling system 302, may generate a path for a tool-head, included inthe three-dimensional extrusion printer 318, to print the structuresincluded in the object represented by the three-dimensional model 304.The path generation module 310 may generate a path for a slice in thethree-dimensional model 304. In some examples, the path generationmodule 310 may generate a path for each slice in the three-dimensionalmodel 304. The path generation module 310 may use one or more of thesteps described with reference to FIG. 2 to generate a path for thetool-head.

The path generation module 310 may generate a path for a slice in thethree-dimensional model 304 to which the surface analysis module 308added data for surface supports, e.g., after analysis of thethree-dimensional model 304 by the angle generation module 306 and thesurface analysis module 308 and creation of the hollow shell. In someexamples, the path generation module 310 may generate a path for a slicein the three-dimensional model 304 for which the surface analysis module308 has not generated any support data. For instance, the pathgeneration module 310 may analyze the three-dimensional model 304without either the angle generation module 306 or the surface analysismodule 308 analyzing any data for the three-dimensional model 304.

The path generation module 310 can use material properties database 314when generating the path for the slice. For example, the path generationmodule 310 determines a cooling time for a particular material that willbe deposited in the slice by retrieving property data for the materialfrom the material properties database 314.

In some examples, the path generation module 310 uses configurationproperties of the three-dimensional extrusion printer 318 whengenerating the path for the slice. For instance, the path generationmodule 310 accesses the three-dimensional printer configuration database312 to determine a temperature at which the three-dimensional extrusionprinter 318 will deposit the material, a temperature of an atmosphere inwhich the material will be deposited, or both. The path generationmodule 310 can use one or more temperatures to determine the path forthe slice.

The three-dimensional modelling system 302 may generate multiple slicesof the three-dimensional model. Each of the slices may include data formultiple structures of the object represented by the respective slice.The three-dimensional modelling system 302 may generate, for each of theslices, tool path data for each of the slices that indicates a path fora tool-head to create the structures represented by the slice.

The three-dimensional modelling system 302 may provide the data for eachof the slices to the three-dimensional extrusion printer 318 to causethe three-dimensional extrusion printer 318 to generate the respectiveportion of the object. For instance, the three-dimensional modellingsystem 302 may provide a first slice to the three-dimensional extrusionprinter 318. The three-dimensional extrusion printer 318 may use thefirst slice to print the structures represented by the first slice. Thethree-dimensional modelling system 302 may sequentially provide thethree-dimensional extrusion printer with subsequent slices to cause thethree-dimensional extrusion printer to create corresponding structuresof the object using the subsequent slices. For instance, thethree-dimensional extrusion printer 318 may use each of the subsequentslices to add another layer to the printed portion of the object untilthe object is completed.

In some implementations, the three-dimensional modelling system 302 maybe included in or be part of the three-dimensional extrusion printer318. For instance, the three-dimensional extrusion printer 318 mayreceive the three-dimensional model 304 from the client device 316 andstore the three-dimensional model 304 in memory. The three-dimensionalextrusion printer 318 may use the angle generation module 306, thesurface analysis module 308, the path generation module 310, or acombination of two or more of these, to analyze the three-dimensionalmodel 304. The three-dimensional extrusion printer 318 may use data forthe analyzed three-dimensional model 304 to create an object representedby the three-dimensional model 304.

The three-dimensional modelling system 302 is an example of a systemimplemented as computer programs on one or more computers in one or morelocations, in which the systems, components, and techniques described inthis document are implemented. The client device 316 may includepersonal computers, mobile communication devices, and other devices thatcan send and receive data over a network 320. The network 320, such as alocal area network (LAN), wide area network (WAN), the Internet, or acombination thereof, connects the client device 316, three-dimensionalmodelling system 302, and the three-dimensional extrusion printer 318.The three-dimensional modelling system 302 may use a single servercomputer or multiple server computers operating in conjunction with oneanother, including, for example, a set of remote computers deployed as acloud computing service.

In some examples, the environment 300 does not include a separatethree-dimensional modelling system 302 and client device 316. Forinstance, the three-dimensional modelling system 302 may provide thethree-dimensional model 304 directly to the three-dimensional extrusionprinter 318 without receiving the three-dimensional model 304 from aseparate device, e.g., the client device 316. In these examples, thethree-dimensional modelling system 302 can connect directly to thethree-dimensional extrusion printer 318 or can connect to thethree-dimensional extrusion printer through any appropriate type ofnetwork, e.g., a LAN.

FIG. 4 is a flow diagram of a process 400 for generating data for infillstructures that will support surfaces of an object. For example, theprocess 400 can be used by the three-dimensional modelling system 302from the environment 300.

A modelling system receives a three-dimensional model of an object to becreated by a three-dimensional extrusion printer (402). For instance,the modelling system receives the three-dimensional model from a clientdevice. In some examples, the modelling system may receive thethree-dimensional model from memory. The three-dimensional modelincludes only data representing exterior surfaces of the object thatwill be a solid object when printed.

The modelling system may determine determining a hollow shell for thethree-dimensional model that includes a plurality of interior surfaces(403). For instance, the modelling system determines an exterior shellfor the three-dimensional model that includes a hollow aperture on theinside that reduces the material requirements for creating the object.

The modelling system determines, for each of the plurality of interiorsurfaces of the object, an angle of the respective interior surface(404). For example, the modelling system determines each of the interiorsurfaces of the object represented in the three-dimensional model. Themodelling system may use any appropriate method to determine the angleof a particular interior surface. The surfaces may be polygon meshes orany other appropriate type of surface for the object.

In some implementations, when a surface is not flat, the modellingsystem may determine multiple angles for the surface. The modellingsystem may divide the non-flat surface into multiple sections. Each ofthe sections may have the same angle, e.g., a single angle, or multipleangles within a predetermined threshold value of the other angles forthe section. For instance, the modelling system may divide a non-flatsurface into multiple sections each of which have angles within thepredetermined threshold value of the other angles for the respectivesection. The modelling system may determine, for each of the multiplesections, an average angle for the section. The modelling system may usethe average angle for the section when analyzing the section. In someexamples, the modelling system may determine, for each of the multiplesections, a largest angle for the section. In these examples, themodelling system may use the largest angle for the section whenanalyzing the section. For instance, when the modelling systemdetermines that a particular section has three angles, 42°, 43.4°, and44.2°, the modelling system may select 44.2° as the angle for theparticular section.

The modelling system determines a configuration of the three-dimensionalextrusion printer (406). For instance, the modelling system maydetermine settings of a print-head included in the three-dimensionalextrusion printer, settings of the three-dimensional extrusion printer,or both, that will be used to create the object using thethree-dimensional model. Some examples of settings for athree-dimensional extrusion printer include whether the printer includesa cooling fan directed toward the print-head, whether the depositionchamber in the printer is heated, the temperature of the depositionchamber, a diameter of an extruder nozzle in the print-head, printspeed, bead diameter, and layer height.

The modelling system determines a material that the three-dimensionalextrusion printer will use to create the object (408). The modellingsystem may determine that the material is a plastic, a metal, or anotherappropriate material.

The modelling system determines a threshold angle using theconfiguration, a property of the material, or both (410). For example,the modelling system may use the configuration of the three-dimensionalextrusion printer, the property of the material, or both, as input todetermine the threshold angle. The modelling system may determine afirst value for the threshold angle when the material is a firstmaterial, e.g., plastic, and a second value for the threshold angle whenthe material is a second material, e.g., metal. The first value may begreater than the second value. For instance, the modelling system maydetermine that a first viscosity of a first material, e.g., a plastic,is lower than a second viscosity of a second material, e.g., a metal,and use a first threshold angle for the first material that is a largerangle than a second threshold angle for the second material.

The modelling system compares the angle of the interior surface with thethreshold angle (412). For instance, the modelling system compares avalue of the angle of the interior surface with a value for thethreshold angle.

The modelling system determines whether the angle satisfies thethreshold angle (414). The modelling system may determine whether avalue of the angle is less than a value of the threshold angle. In someexamples, the modelling system may determine whether a value of theangle is less than or equal to a value of the threshold angle. Themodelling system may use a result of the comparison to determine whetherthe angle satisfies the threshold angle.

In some implementations, the modelling system may perform steps 412 and414 for multiple surfaces. For instance, the modelling system maycompare, for each of the multiple surfaces, a value of the respectiveangle with a value of the threshold angle and determine whether thevalue of the respective angle satisfies the value of the threshold angleusing a result of the comparison. The modelling system may determine,for each surface in a first subset of the multiple surfaces, that theangle does not satisfy the threshold angle. The modelling system maydetermine, for each surface in a second subset of the multiple surfaces,that the angle does not satisfy the threshold angle. The second subsetis a different subset of surfaces from the multiple surfaces than thefirst subset. The second subset is a disjoint subset from the firstsubset.

The surfaces may be exterior surfaces. In some implementations, thesurfaces are interior surfaces, e.g., and not exterior surfaces. In someexamples, the multiple surfaces may include both interior surfaces andexterior surfaces.

In response to determining that the surface satisfies the thresholdangle, the modelling system determines an infill structure for aninterior structure to be located inside the object and extending throughone or more layers of the three-dimensional model up to the interiorsurface (416). The layers may be slices of the three-dimensional model.The modelling system may determine any appropriate type of infillstructure for an interior structure. For example, the modelling systemmay use a hexagonal infill structure for the interior structure. In someexamples, the modelling system may use a rectilinear infill structure, aconcentric infill structure, a honeycomb infill structure, or acombination of two or more of these. The modelling system may select aninfill structure to minimize material necessary to create the interiorstructure while providing an appropriate strength for the interiorstructure.

When created by a three-dimensional printer, the interior structuresupports the corresponding surface. For instance, if thethree-dimensional printer were to try to create the surface without theinterior structure, the surface may not be able to support itself, e.g.,would collapse. The creation of the interior structure in thethree-dimensional model allows the three-dimensional printer to createthe surface using data for the three-dimensional model.

The interior structure may extend through multiple slices of thethree-dimensional model. The modelling system may create the interiorstructure between a lower surface below the surface and extendingthrough each slice of the three-dimensional model up to the surface. Forinstance, the interior structure may extend through all slices betweenthe lower surface below the surface and the surface. In some examples,the modelling system creates an interior structure, in thethree-dimensional model, that extends from a bottom surface of thethree-dimensional model to the surface, e.g., through each layer of themodel between the bottom surface and the surface.

In response to determining that the surface does not satisfy thethreshold angle, the modelling system skips generation of any infillstructure (418). For instance, the modelling system determines not togenerate an interior structure, or a corresponding infill structure foran interior structure, for the surface.

The modelling system may store data indicating which of the surfaces themodelling system has analyzed. For instance, the data may indicate thatthe modelling system compared a value of an angle for the surface with avalue for a threshold angle. The modelling system may use the data tolater determine that the modelling system analyzed the surface, whetheror not the angle for the surface satisfies the threshold angle, or both.The data may indicate whether the surface needs a support or themodelling system added a support to the three-dimensional model.

The modelling system determines whether there are interior surfaces leftto analyze (420). For example, the modelling system uses the data thatindicates which of the surfaces the modelling system has analyzed todetermine whether or not there are more surfaces in thethree-dimensional model to analyze. The modelling system may analyzeonly interior surfaces of the three-dimensional model. In theseexamples, the modelling system determines whether there are interiorsurfaces to analyze. The modelling system may analyze only interiorsurfaces. In these examples, the modelling system determines whetherthere are interior surfaces to analyze. In some implementations, themodelling system analyzes both interior surfaces and interior surfaces.In these implementations, the modelling system determines whether thereare any interior surfaces or any interior surfaces left to analyze.

The modelling system generates data that represents each of thedetermined infill structures for use by the three-dimensional extrusionprinter with the three-dimensional model to create the object (422). Forinstance, the modelling system uses the infill structures for theinterior structures to generate the data that represents the infillstructure. The data indicates the slices of the three-dimensional modelthrough which the interior structure, with the infill structure, passes.In some examples, the modelling system may perform part of the step 422when determining the infill structure, e.g., as part of step 416. Forexample, when the modelling system determines the infill structure for aparticular interior structure, the modelling system may generate thedata that represents the infill structure for the particular interiorstructure. The modelling system may add the data for the infillstructures to the three-dimensional model.

The order of steps in the process 400 described above is illustrativeonly, and generating data for infill structures that will supportsurfaces of the object can be performed in different orders. Forexample, the modelling system may determine the material that athree-dimensional extrusion printer will use to create the objectrepresented by the three-dimensional model before determining aconfiguration of the three-dimensional extrusion printer.

In some implementations, the process 400 can include additional steps,fewer steps, or some of the steps can be divided into multiple steps.For example, the modelling system may perform steps 402, 404, 416, 418,and 422 without performing the other steps of the process 400. In someexamples, the modelling system may perform steps 402 and 404, a portionof step 410, and steps 412 through 422. For instance, the modellingsystem may determine, as the portion of step 410, the threshold angleusing the configuration of the three-dimensional printer, the propertyof the material, both, or neither. In some examples, the modellingsystem may send data for the three-dimensional model to athree-dimensional extrusion printer to cause the three-dimensionalextrusion printer to create an object represented by thethree-dimensional object.

In some implementations, the modelling system may compare the data thatrepresents the determined infill structures and the hollow shell withthe data for a solid object to determine whether creation of the objectusing the infill structures and the hollow shell satisfies one or moreefficiency criteria. The efficiency criteria may include a quantity ofmaterial saved by creating the object with the hollow shell and theinfill structures instead of creating a solid object. The efficiencycriteria may include an amount of time saved by creating the object withthe hollow shell and the infill structures instead of creating a solidobject. The efficiency criteria may include a quantity of beads thatwill not be deposited by creating the object with the hollow shell andthe infill structures instead of creating a solid object. The efficiencycriteria may include a value that indicate whether the modified objectcreated using the hollow shell and the infill structures will have astrength within a threshold value of the original solid obj ect.

When the modelling system determines that an efficiency for the modifiedobject, e.g., for the infill structures and the hollow shell, satisfiesa threshold efficiency, the modelling system may send the data for themodified object to a three-dimensional printer for creation of theobject with one or more apertures in the object. When the modellingsystem determines that an efficiency for the modified object does notsatisfy the threshold efficiency, the modelling system sends data for anunmodified object, e.g., the solid object, to a three-dimensionalprinter for creation of the solid object.

FIG. 5 is a flow diagram of a process 500 for generating a tool-headpath. For example, the process 500 can be used by the three-dimensionalmodelling system 302 from the environment 300.

A modelling system receives a three-dimensional model of an object to becreated by a three-dimensional extrusion printer that includes atool-head that will create at least a portion of the object (502). Forinstance, the modelling system receives the three-dimensional model froma client device. In some examples, the modelling system may receive thethree-dimensional model from memory.

The modelling system determines a plurality of infill structures in aslice of the object (504). The modelling system may create multipleslices of the three-dimensional model. For each of the slices, themodelling system determines multiple infill structures in the slice.

The modelling system determines a first portion of a path for thetool-head that will cause the tool-head to deposit material forming thefirst infill structure from the plurality of infill structures during afirst time period (506). For examples, the modelling system selects oneof the multiple infill structures as the first infill structure. Themodelling system may select the first infill structure, from themultiple infill structures randomly.

In some examples, the modelling system may select, as the first infillstructure, an infill structure from a region in the slice with a highestdensity of infill structures, e.g., a highest quantity of infillstructures. For instance, when the slice is part of a three-dimensionalscale model of a house, a particular region of the house, e.g., abedroom, may have a higher density of infill structures than anotherregion of the house, e.g., a living room. The modelling system maydetermine the region with the highest density of infill structuresbecause there are likely to be more infill structures that are adjacentto other infill structures in that region. The modelling system mayselect an infill structure that is adjacent to a highest quantity ofother infill structures.

The modelling system may determine a material that the three-dimensionalextrusion printer will use to create the object. In some examples, themodelling system may determine a material that the three-dimensionalextrusion printer will use to create the first infill structure, e.g.,in examples in which the object is created using multiple differentmaterials.

The modelling system may determine a cooling time for the material usinga first temperature at which the material will be deposited, a secondtemperature of an area in which the material will be deposited, one ormore properties of the material, or a combination of two or more ofthese. The second temperature may include multiple second temperatures.The properties of the material may include a cooling time for thematerial. The properties of the material may include any appropriatetype of material properties.

The area in which the material will be deposited may include a chamberin which the three-dimensional extrusion printer creates the firstinfill structure. The second temperature may include a temperature ofthe chamber. The area may include atmosphere or other gases. The secondtemperature may include a temperature of the atmosphere or other gases.

The second temperature may be a temperature of a particular materialonto which the material will be deposited. In some examples, themodelling system may determine a temperature of a base that supports theobject during creation as a temperature of an area in which the materialwill be deposited. The modelling system may determine a temperature ofanother material that has been deposited, another material that will bedeposited, or both, as a temperature of an area in which the materialwill be deposited. In some examples, the area in which the material willbe deposited may have multiple second temperatures, e.g., one for a gasin which the material will be deposited and one for the particularmaterial onto which the material will be deposited.

One or more of the temperatures may be predicted temperatures. Forinstance, the modelling system may determine the temperatures before thethree-dimensional extrusion printer creates the object. In theseexamples, the temperatures are predicted temperatures. In some examples,the modelling system may determine the temperatures while thethree-dimensional extrusion printer creates the object. In theseexamples, some of the temperatures may be actual temperatures, some ofthe temperatures may be predicted temperatures, or both. For instance,the modelling system may provide the three-dimensional extrusion printerwith a first slice path for a tool-head, included in thethree-dimensional extrusion printer. While the tool-head uses the firstslice path to create a first slice of the object, the modelling systemmay create a second slice path for a second slice of the object that isadjacent to and directly above the first slice. The modelling system mayuse data from the creation of the first slice to determine the secondslice path, e.g., data that indicates one or more actual temperaturesfor the three-dimensional extrusion printer, the object being created bythe three-dimensional extrusion printer, or both.

The modelling system may determine a duration for a second time periodusing the cooling time for the material. The modelling system maydetermine the duration to allow the material sufficient time to coolbefore deposition of another material adjacent to the material. Forinstance, the modelling system may select the second time period suchthat the material is less likely to warp when another material isdeposited adjacent to the material.

In some implementations, the modelling system may determine a depositionrate for the first infill structure, e.g., the first portion of thepath. The modelling system may determine the deposition rate using aduration of the first time period, the duration of the second timeperiod, a property of the material, or a combination of two or more ofthese.

The modelling system selects another infill structure from the pluralityof infill structures (508). The modelling system may use any appropriatemethod to select the other infill structure. For example, the modellingsystem may select the other infill structure at random. The modellingsystem may assign, to each of the infill structures, a number, e.g., anidentifier. The modelling system may select an infill structure atrandom by generating a random number and determining the identifier thatis closest to, or the same as, the random number. In some examples, themodelling system may select an infill structure as the other infillstructure that is adjacent to a highest quantity of other infillstructures, e.g., for which the modelling system has not determinedrespective portions of the path.

The modelling system determines whether the other infill structure is asecond infill structure that is not adjacent to the first infillstructure (510). For example, the modelling system analyzes theboundaries of the other infill structure to determine whether one of theboundaries of the second infill structure is adjacent to a boundary ofthe first infill structure. In some examples, the modelling system mayselect an infill structure that is adjacent to a highest quantity ofother infill structures and that is not adjacent to the first infillstructure.

If one of the boundaries is adjacent to a boundary of the previousinfill structure, e.g., the first infill structure, the modelling systemselects a different infill structure, e.g., repeats step 508. When themodelling system determines that there is only one infill structure leftand that the one remaining infill structure is adjacent to the previousinfill structure, the modelling system may begin the process 500 again,e.g., with a different initial infill structure, a different path tocreate the various infill structures, or both. In some examples, whenthe modelling system determines that there is only one infill structureleft and that the one remaining infill structure is adjacent to theprevious infill structure, the modelling system adds a wait period forthe tool-head before the tool-head will create the last infillstructure. For example, the modelling system adds instructions to datathat represents the path for the current slice that indicates that thetool-head should wait for a particular period of time before beginningdeposition of the last infill structure. In some examples, when themodelling system determines that there is only one infill structure leftand that the one remaining infill structure is adjacent to the previousinfill structure, the modelling system may change a deposition rate ofone or more other infill structures so that deposition of the lastinfill structure will begin after the infill structures adjacent to thelast infill structure have cooled for the determined cooling periods.

When the modelling system determines that the second infill structure isnot adjacent to the first infill structure, the modelling systemdetermines a second portion of the path to cause the tool-head todeposit material forming the second infill structure during a secondtime period after the first time period (512). The modelling system maydetermine a quantity of beads for the tool-head to deposit when formingthe second infill structure. The modelling system may use the quantityof beads to determine the second portion of the path. The modellingsystem may determine at which end of the second infill structure thetool-head should begin to deposit material for the second infillstructure, e.g., an end closest to a last location at which thetool-head will deposit material for the first infill structure. Themodelling system may determine a direction for the second portion of thepath along which the tool-head will move to form the second infillstructure. The modelling system may use the determined end of the secondinfill structure, the direction for the second portion of the path, orboth, to determine at least part of the second portion of the path.

In some implementations, the modelling system may determine a depositionrate for the second infill structure, e.g., the second portion of thepath. The modelling system may determine the deposition rate using aduration of the second time period, a property of the material that willform the second infill structure, or a combination of two or more ofthese. In some examples, the modelling system may determine thedeposition rate for the second infill structure using a size of thesecond infill structure, an amount of material that will be deposited toform the second infill structure, or both.

The modelling system may adjust the deposition rate based on a currentduration of time to deposit material for the second infill structure andthe determined duration for the second time period. For instance, whenthe current duration is less than the determined duration for the secondtime period the modelling system may adjust the deposition rate toreduce or increase the current duration. In some examples, when thecurrent duration is greater than the determined duration for the secondtime period, the modelling system may determine whether or not to changethe current duration, e.g., the modelling system might not change thecurrent duration.

The modelling system determines whether a duration for the tool-head tomove through the second portions of the path satisfies the second timeperiod (514). For example, the modelling system determines whether atime for the tool-head to deposit material for the second infillstructure satisfies, e.g., is greater than or equal to, the duration forthe second time period. In some examples, the duration satisfies thesecond time period when the duration is greater than a predeterminedduration of the second time period.

Since the modelling system determined a duration of the second timeperiod to allow the first infill structure to cool before deposition ofthe third infill structure, adjacent to the first infill structure, bythe tool-head of the three-dimensional extrusion printer, the modellingsystem determines whether the second portion of the path causes thetool-head to deposit material during the entirety of the second timeperiod or whether more time is necessary to allow the first infillstructure to cool. The modelling system may use a time period for thetool-head to move from the first infill structure to the second infillstructure, a time period for the tool-head to move from the secondinfill structure to a third infill structure, or both, when determiningwhether the duration for the tool-head to move through the secondportions of the path satisfies the second time period. For instance, themodelling system may add one or more durations of the movement timeperiods with the duration for deposition of the second infill structure,as the second portion of the path, to determine whether the duration ofthe second portion of the path satisfies the second time period.

When the modelling system determines that the duration for the tool-headto move through the second portions of the path does not satisfy thesecond time period, the modelling system selects another infillstructure and generates a path for the other infill structure. Forinstance, the modelling system performs steps 508 through 512 until theduration for the tool-head to move through all of the second portions ofthe path satisfies the second time period. The duration for the secondportions of the path satisfies the second time period when a durationthat the tool-head will take to move to each of the second infillstructures, deposit material for the second infill structures that arenot adjacent to the first infill structure, or both, is greater than,equal to, or both, the predetermined duration for the second timeperiod.

The modelling system selects a third infill structure, from theplurality of infill structures, that is adjacent to the first infillstructure in the slice (516). The modelling system may determine theinfill structures in the slice that are adjacent to the first infillstructure. The determined infill structures may be infill structures forwhich the modelling system has not yet generated a portion of the pathfor the slice that will cause the tool-head to deposit material to formthe corresponding infill structure. If there is only one infillstructure in the slice for which the modelling system has not generateda portion of the path for the slice, the modelling system may select theone infill structure. When there are multiple infill structures in theslice for which the modelling system has not yet generated a portion ofthe path for the slice, the modelling system may select one of themultiple infill structures at random. In some examples, when there aremultiple infill structures in the slice for which the modelling systemhas not generated a portion of the path for the slice, the modellingsystem may select one of the multiple infill structures that is adjacentto the first infill structure and a highest quantity of other infillstructures for which the modelling system has not created portions ofthe path for the slice.

The modelling system determines a third portion of the path to cause thetool-head to deposit material forming the third infill structure duringa third time period after the second time period (518). For instance,the modelling system determines an end of the third infill structuresthat is closest to a last location at which the tool-head will depositmaterial for the second infill structure. The modelling system may usethe determined end as the beginning of the third portion of the path.

In some implementations, the process 500 can include additional steps,fewer steps, or some of the steps can be divided into multiple steps.For example, the modelling system may determine a duration of time forwhich a material that will be deposited in a previous layer has cooled.When the three-dimensional printer will create multiple layers for aparticular infill structure, the modelling system may determine when thethree-dimensional printer will deposit material for the particularinfill structure and directly below an area in a current slice for theparticular infill structure. When a duration of time for the material inthe previous slice to cool does not satisfy a threshold duration, e.g.,the material in the previous layer will not likely have cooledsufficiently, the modelling system may select another infill structurefor the path.

The modelling system may repeat the process 500, or portions of theprocess 500, for all infill structures in a current slice. For instance,the modelling system may select a first infill structure and then repeatthe steps for selection of second infill structures and third infillstructures until the modelling system generates portions of the path forall of the infill structures in a current slice.

The modelling system may provide data for the slice and the path to athree-dimensional extrusion printer after generation of the path. Forinstance, the modelling system may generate paths for all slices of athree-dimensional model and then provide data representing the slicesand the paths to the three-dimensional extrusion printer. In someexamples, the modelling system may generate a path for a first slice andprovide data for the first slice and the path to a three-dimensionalextrusion printer, e.g., to cause the three-dimensional extrusionprinter to create a portion of an object represented by the first slice.The modelling system then generates a path for a second slice that isdirectly adjacent to and on top of the first slice. The modelling systemprovides the generated path and data for the second slice to thethree-dimensional extrusion printer.

Embodiments of the subject matter and the functional operationsdescribed in this specification can be implemented in digital electroniccircuitry, in tangibly-embodied computer software or firmware, incomputer hardware, including the structures disclosed in thisspecification and their structural equivalents, or in combinations ofone or more of them. Embodiments of the subject matter described in thisspecification can be implemented as one or more computer programs, i.e.,one or more modules of computer program instructions encoded on atangible non-transitory program carrier for execution by, or to controlthe operation of, data processing apparatus. Alternatively or inaddition, the program instructions can be encoded on anartificially-generated propagated signal, e.g., a machine-generatedelectrical, optical, or electromagnetic signal, that is generated toencode information for transmission to suitable receiver apparatus forexecution by a data processing apparatus. The computer storage mediumcan be a machine-readable storage device, a machine-readable storagesubstrate, a random or serial access memory device, or a combination ofone or more of them.

The term “data processing apparatus” refers to data processing hardwareand encompasses all kinds of apparatus, devices, and machines forprocessing data, including by way of example a programmable processor, acomputer, or multiple processors or computers. The apparatus can also beor further include special purpose logic circuitry, e.g., an FPGA (fieldprogrammable gate array) or an ASIC (application-specific integratedcircuit). The apparatus can optionally include, in addition to hardware,code that creates an execution environment for computer programs, e.g.,code that constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them.

A computer program, which may also be referred to or described as aprogram, software, a software application, a module, a software module,a script, or code, can be written in any form of programming language,including compiled or interpreted languages, or declarative orprocedural languages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment. A computer program may, butneed not, correspond to a file in a file system. A program can be storedin a portion of a file that holds other programs or data, e.g., one ormore scripts stored in a markup language document, in a single filededicated to the program in question, or in multiple coordinated files,e.g., files that store one or more modules, sub-programs, or portions ofcode. A computer program can be deployed to be executed on one computeror on multiple computers that are located at one site or distributedacross multiple sites and interconnected by a communication network.

The processes and logic flows described in this specification can beperformed by one or more programmable computers executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit).

Computers suitable for the execution of a computer program include, byway of example, general or special purpose microprocessors or both, orany other kind of central processing unit. Generally, a centralprocessing unit will receive instructions and data from a read-onlymemory or a random access memory or both. The essential elements of acomputer are a central processing unit for performing or executinginstructions and one or more memory devices for storing instructions anddata. Generally, a computer will also include, or be operatively coupledto receive data from or transfer data to, or both, one or more massstorage devices for storing data, e.g., magnetic, magneto-optical disks,or optical disks. However, a computer need not have such devices.Moreover, a computer can be embedded in another device, e.g., a mobiletelephone, a personal digital assistant (PDA), a mobile audio or videoplayer, a game console, a Global Positioning System (GPS) receiver, or aportable storage device, e.g., a universal serial bus (USB) flash drive,to name just a few.

Computer-readable media suitable for storing computer programinstructions and data include all forms of non-volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks,e.g., internal hard disks or removable disks; magneto-optical disks; andCD-ROM and DVD-ROM disks. The processor and the memory can besupplemented by, or incorporated in, special purpose logic circuitry.

To provide for interaction with a user, embodiments of the subjectmatter described in this specification can be implemented on a computerhaving a display device, e.g., LCD (liquid crystal display), OLED(organic light emitting diode) or other monitor, for displayinginformation to the user and a keyboard and a pointing device, e.g., amouse or a trackball, by which the user can provide input to thecomputer. Other kinds of devices can be used to provide for interactionwith a user as well; for example, feedback provided to the user can beany form of sensory feedback, e.g., visual feedback, auditory feedback,or tactile feedback; and input from the user can be received in anyform, including acoustic, speech, or tactile input. In addition, acomputer can interact with a user by sending documents to and receivingdocuments from a device that is used by the user; for example, bysending web pages to a web browser on a user’s device in response torequests received from the web browser.

Embodiments of the subject matter described in this specification can beimplemented in a computing system that includes a back-end component,e.g., as a data server, or that includes a middleware component, e.g.,an application server, or that includes a front-end component, e.g., aclient computer having a graphical user interface or a Web browserthrough which a user can interact with an implementation of the subjectmatter described in this specification, or any combination of one ormore such back-end, middleware, or front-end components. The componentsof the system can be interconnected by any form or medium of digitaldata communication, e.g., a communication network. Examples ofcommunication networks include a local area network (LAN) and a widearea network (WAN), e.g., the Internet.

The computing system can include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other. In someembodiments, a server transmits data, e.g., an HyperText Markup Language(HTML) page, to a user device, e.g., for purposes of displaying data toand receiving user input from a user interacting with the user device,which acts as a client. Data generated at the user device, e.g., aresult of the user interaction, can be received from the user device atthe server.

An example of one such type of computer is shown in FIG. 6 , which showsa schematic diagram of a computer system 600. The system 600 can be usedfor the operations described in association with any of thecomputer-implemented methods described previously, according to someimplementations. The system 600 includes a processor 610, a memory 620,a storage device 630, and an input/output device 640. Each of thecomponents 610, 620, 630, and 640 are interconnected using a system bus650. The processor 610 is capable of processing instructions forexecution within the system 600. In some implementations, the processor610 is a single-threaded processor. In other implementations, theprocessor 610 is a multi-threaded processor. The processor 610 iscapable of processing instructions stored in the memory 620 or on thestorage device 630 to display graphical information for a user interfaceon the input/output device 640.

The memory 620 stores information within the system 600. In someimplementations, the memory 620 is a non-transitory computer-readablemedium. In some implementations, the memory 620 is a volatile memoryunit. In other implementations, the memory 620 is a non-volatile memoryunit.

The storage device 630 is capable of providing mass storage for thesystem 600. In some implementations, the storage device 630 is anon-transitory computer-readable medium. In various differentimplementations, the storage device 630 may be a floppy disk device, ahard disk device, an optical disk device, a tape device, or a solidstate memory device.

The input/output device 640 provides input/output operations for thesystem 600. In some implementations, the input/output device 640includes a keyboard and/or pointing device. In other implementations,the input/output device 640 includes a display unit for displayinggraphical user interfaces.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments. Certain features that are described in thisspecification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable subcombination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various system modulesand components in the embodiments described above should not beunderstood as requiring such separation in all embodiments, and itshould be understood that the described program components and systemscan generally be integrated together in a single software product orpackaged into multiple software products.

Particular embodiments of the subject matter have been described. Otherembodiments are within the scope of the following claims. For example,the actions recited in the claims can be performed in a different orderand still achieve desirable results. As one example, the processesdepicted in the accompanying figures do not necessarily require theparticular order shown, or sequential order, to achieve desirableresults. In some cases, multitasking and parallel processing may beadvantageous.

What is claimed is:
 1. (canceled)
 2. A computer-implemented methodcomprising: determining, by a three-dimensional modelling system, one ormore infill structures for a three-dimensional model of a solid object,wherein the one or more infill structures are located in an interior ofa hollow shell of the three-dimensional model, the hollow shell and theone or more infill structures together defining a modified object forthe three-dimensional model; determining, by the three-dimensionalmodelling system, that creation of the modified object, by thethree-dimensional printer, using the one or more infill structures andthe hollow shell satisfies one or more efficiency criteria by comparingdata representing the one or more infill structures and the hollow shellof the modified object with data for the solid object; and providingdata for the one or more infill structures and the hollow shell that isuseable to cause the three-dimensional printer to create the modifiedobject after determination that the one or more efficiency criteria aresatisfied.
 3. The computer-implemented method of claim 2, wherein theone or more efficiency criteria comprise a strength of the modifiedobject being within a threshold value.
 4. The computer-implementedmethod of claim 3, comprising determining the threshold value for thestrength based on a material to be used by the three-dimensional printerto create the modified object and pressures to be applied to themodified object.
 5. The computer-implemented method of claim 3, whereinthe one or more efficiency criteria further comprise (i) a quantity ofmaterial saved by creating the modified object with the hollow shell andthe one or more infill structures instead of creating the solid object,and (ii) an amount of time saved by creating the modified object withthe hollow shell and the one or more infill structures instead ofcreating the solid object.
 6. The computer-implemented method of claim3, wherein determining the one or more infill structures comprisesbalancing a material necessary to support a top section of the modifiedobject with a time necessary to deposit the material.
 7. Thecomputer-implemented method of claim 2, wherein determining the one ormore infill structures comprises selecting an infill structure tominimize material necessary to create the interior of the hollow shellwhile providing an appropriate strength.
 8. The computer-implementedmethod of claim 7, wherein determining the one or more infill structuresby selecting an infill structure comprises: analyzing interior surfaceangles formed by the hollow shell; selecting a first type of infillstructure when an angle of an interior surface of the hollow shell fallswithin a first angle range; and selecting a second type of infillstructure when an angle of an interior surface of the hollow shell fallswithin a second angle range.
 9. The computer-implemented method of claim2, wherein determining the one or more infill structures comprises:analyzing interior surface angles formed by the hollow shell; andskipping generation of any infill structure for at least one interiorsurface of the hollow shell having an angle that does not satisfy athreshold angle.
 10. The computer-implemented method of claim 9,comprising determining the threshold angle based on a configuration ofthe three-dimensional printer and a material to be used by thethree-dimensional printer to create the modified object.
 11. Thecomputer-implemented method of claim 9, comprising determining differentthicknesses for different portions of the hollow shell depending on alocation of each of the different portions of the hollow shell.
 12. Thecomputer-implemented method of claim 11, comprising determining aminimum thickness for the hollow shell based on a material of themodified object and expected forces that will be applied to the modifiedobject.
 13. The computer-implemented method of claim 2, wherein theproviding comprises: generating slices of the three-dimensional model;generating tool path data in each of the slices, the tool path dataindicating paths for a tool-head in the three-dimensional printer; andsending the tool path data to the three-dimensional printer, therebycausing the three-dimensional printer to create the modified object bymoving the tool-head in accordance with the paths.
 14. Thecomputer-implemented method of claim 13, wherein generating the toolpath data comprises, in at least one of the slices, splitting the sliceinto regions for separate printing of each of the regions so that forcesin each of the regions, created because of the printing, manifest at asmaller spatial scale compared to not splitting the slice into theregions for separate printing.
 15. The computer-implemented method ofclaim 13, wherein determining the one or more infill structurescomprises using an open cell lattice infill in which X-Y sectionscontain no toolpaths connecting unit cells, resulting in smallerdeposited beads of material during printing, which localizes contractiveforces on the unit cells as the deposited beads of material cool. 16.The computer-implemented method of claim 2, wherein determining the oneor more infill structures comprises determining sizes of respectiveregions of infill in a slice of the three-dimensional model using adetermined maximum fill line length.
 17. The computer-implemented methodof claim 16, wherein determining the sizes of the respective regions ofinfill comprises adjusting the sizes based on a type of material to beused to create the one or more infill structures in the respectiveregions.
 18. A non-transitory computer readable storage medium storinginstructions executable by a data processing apparatus and upon suchexecution cause the data processing apparatus to perform operationscomprising: determining one or more infill structures for athree-dimensional model of a solid object, wherein the one or moreinfill structures are located in an interior of a hollow shell of thethree-dimensional model, the hollow shell and the one or more infillstructures together defining a modified object for the three-dimensionalmodel; determining that creation of the modified object, by thethree-dimensional printer, using the one or more infill structures andthe hollow shell satisfies one or more efficiency criteria by comparingdata representing the one or more infill structures and the hollow shellof the modified object with data for the solid object; and providingdata for the one or more infill structures and the hollow shell that isuseable to cause the three-dimensional printer to create the modifiedobject after determination that the one or more efficiency criteria aresatisfied.
 19. The non-transitory computer readable storage medium ofclaim 18, wherein the one or more efficiency criteria comprise astrength of the modified object being within a threshold value.
 20. Thenon-transitory computer readable storage medium of claim 19, wherein theoperations comprise determining the threshold value for the strengthbased on a material to be used by the three-dimensional printer tocreate the modified object and pressures to be applied to the modifiedobject.
 21. The non-transitory computer readable storage medium of claim19, wherein the one or more efficiency criteria further comprise (i) aquantity of material saved by creating the modified object with thehollow shell and the one or more infill structures instead of creatingthe solid object, and (ii) an amount of time saved by creating themodified object with the hollow shell and the one or more infillstructures instead of creating the solid object.
 22. The non-transitorycomputer readable storage medium of claim 19, wherein determining theone or more infill structures comprises balancing a material necessaryto support a top section of the modified object with a time necessary todeposit the material.
 23. The non-transitory computer readable storagemedium of claim 18, wherein determining the one or more infillstructures comprises selecting an infill structure to minimize materialnecessary to create the interior of the hollow shell while providing anappropriate strength.
 24. The non-transitory computer readable storagemedium of claim 23, wherein determining the one or more infillstructures by selecting an infill structure comprises: analyzinginterior surface angles formed by the hollow shell; selecting a firsttype of infill structure when an angle of an interior surface of thehollow shell falls within a first angle range; and selecting a secondtype of infill structure when an angle of an interior surface of thehollow shell falls within a second angle range.
 25. The non-transitorycomputer readable storage medium of claim 18, wherein determining theone or more infill structures comprises: analyzing interior surfaceangles formed by the hollow shell; and skipping generation of any infillstructure for at least one interior surface of the hollow shell havingan angle that does not satisfy a threshold angle.
 26. The non-transitorycomputer readable storage medium of claim 25, wherein the operationscomprise determining the threshold angle based on a configuration of thethree-dimensional printer and a material to be used by thethree-dimensional printer to create the modified object.
 27. Thenon-transitory computer readable storage medium of claim 25, wherein theoperations comprise determining different thicknesses for differentportions of the hollow shell depending on a location of each of thedifferent portions of the hollow shell.
 28. The non-transitory computerreadable storage medium of claim 27, wherein the operations comprisedetermining a minimum thickness for the hollow shell based on a materialof the modified object and expected forces that will be applied to themodified object.
 29. The non-transitory computer readable storage mediumof claim 18, wherein the providing comprises: generating slices of thethree-dimensional model; generating tool path data in each of theslices, the tool path data indicating paths for a tool-head in thethree-dimensional printer; and sending the tool path data to thethree-dimensional printer, thereby causing the three-dimensional printerto create the modified object by moving the tool-head in accordance withthe paths.
 30. The non-transitory computer readable storage medium ofclaim 29, wherein generating the tool path data comprises, in at leastone of the slices, splitting the slice into regions for separateprinting of each of the regions so that forces in each of the regions,created because of the printing, manifest at a smaller spatial scalecompared to not splitting the slice into the regions for separateprinting.
 31. The non-transitory computer readable storage medium ofclaim 29, wherein determining the one or more infill structurescomprises using an open cell lattice infill in which X-Y sectionscontain no toolpaths connecting unit cells, resulting in smallerdeposited beads of material during printing, which localizes contractiveforces on the unit cells as the deposited beads of material cool. 32.The non-transitory computer readable storage medium of claim 18, whereindetermining the one or more infill structures comprises determiningsizes of respective regions of infill in a slice of thethree-dimensional model using a determined maximum fill line length. 33.The non-transitory computer readable storage medium of claim 32, whereindetermining the sizes of the respective regions of infill comprisesadjusting the sizes based on a type of material to be used to create theone or more infill structures in the respective regions.
 34. A systemcomprising: one or more computers; and one or more storage devicescoupled with the one or more computers and on which are storedinstructions; wherein the instructions stored on the one or more storagedevices are configured to cause the one or more computers to determineone or more infill structures for a three-dimensional model of a solidobject, wherein the one or more infill structures are located in aninterior of a hollow shell of the three-dimensional model, the hollowshell and the one or more infill structures together defining a modifiedobject for the three-dimensional model, determine that creation of themodified object, by the three-dimensional printer, using the one or moreinfill structures and the hollow shell satisfies one or more efficiencycriteria by comparing data representing the one or more infillstructures and the hollow shell of the modified object with data for thesolid object, and provide data for the one or more infill structures andthe hollow shell that is useable to cause the three-dimensional printerto create the modified object after determination that the one or moreefficiency criteria are satisfied.
 35. The system of claim 34, whereinthe one or more efficiency criteria comprise a strength of the modifiedobject being within a threshold value.